Introduction of Medical Microbiology: Bacterial Cell

Introduction of Medical Microbiology, Branches of Microbiology; : Bacterial Cell; Essential structures of Bacteria

Transcript

1. Medical Microbiology: Introduction Dr. Md. Abdullah Yusuf Assistant Professor, Dept. of Microbiology National Institute of Neurosciences & Hospital Dhaka, Bangladesh Email: ayusuf75@yahoo.com
2. Learning Objectives Introduction and history of Microbiology • Important events of history • Koch’s postulates • Branches of Medical Microbiology • Role of Microbes in environment & medical science
3. Important events of history • Dutch Biologist “Anton Van Leeuwenhock” discovered “animicules” in a drop of water by his simple microscope in 1674 • Otto Muller (Danish biologist) organized bacteria into genus and species in1774 • In 1840, Friedrich Henle (German pathologist) proposed germ theory of disease
4. Conti… • Robert Koch – Father of medical Microbiology • Luis Pasteur (Father of Modern Microbiology) – identified causative agent of anthrax, rabies, plague, cholera and tuberculosis • Discovery of penicillin – 1928 (Alexander Flemming) • Discovery of sulphanilamide – 1935 (Gerhard Domagk’s) • Discovery of streptomycin – 1928 (Selman Waksman)
5. Koch’s postulates 1. The causative (etiological) agent must be present in all affected organisms – but absent in healthy individuals 2. The agent must be capable of being isolated and cultured in pure form 3. When the cultured agent is introduced to a healthy organism, – the same disease must occur 4. The same causative agent must be isolated again from the affected host
6. Limitation of Koch’s Postulate • Genetic Diseases • Auto-immune Diseases • Non-culturable microbial diseases
7. Branches of Medical Microbiology • Bacteriology – General – Systemic • Virology – General – Systemic • Parasitology – Protogoology – Helminthiology • Mycology • Immunology
8. Difference between Virus And Bactria • Structure • Nucleic Acid • Type of Nucleus • Ribosomes • Nature of Outer Surface • Motility • Method of Replication
9. Eukaryotes and Prokaryotes • Properties • Differences • examples
10. What is bacterium? • Prokaryotic cells – Pro means primitive – Karyote means nuceus • Multiply by binary fission – 1divide to 2 • Devoid of chlorophil • ** single cell, living being, microscopic entity but fantastic in structural organization, reproduction, metabolism and function
11. Eukaryotes • Eu means True (normal) • Karyote means nucleus • Much larger than most prokaryotes • Have subcellular, membrane-bound organelles • Includes all “higher" plants and animals • Microbiology includes – Fungi – Protozoa – Algae – Multicellular Organisms (helminthes)
12. Fungus • Eukaryotic organism • cell walls contains Chitin • Molds are multicellular – masses of mycelia – composed of filaments called hyphae • Yeasts are unicellular
13. Protozoa • Eukaryotes • No Cell Wall • Surround and absorb food • May be motile via – Pseudopods – cilia, or – flagella
14. Algae • Eukaryotes • Cellulose cell walls • Use photosynthesis for energy • Produce molecular oxygen and organic compounds
15. Virus • Acellular • Consist of DNA or RNA • Core is surrounded by a protein coat • Coat may be enclosed in a lipid envelope • Viruses are replicated only when they are in a living host cell • Living
16. Multicellular- helminthes • Eukaryote • Multicellular animals • Parasitic flatworms and round worms are called helminths • Microscopic stages in life cycles
17. Characteristics of Prokaryotes Nuclear level • Absence of – nuclear membrane – Nucleolie – Nucleoplasm – paired multiple chromosome – centriole
18. Conti.. Cytoplasmic level • Absence of membrane bound organelles – Mitochondria – endoplasmic reticulum – golgi complex – Microtubules – Microfilaments
19. Conti.. • Presence of – Ribosome – Plasmid • No protoplasmic streamming in the form of Brownian movement and Tyndall phenomena • No change in definite shape and formation of pseudopodia
20. Characteristics of prokaryotes (Structural) Cell coverings (cell envelope) • Innermost layer – bilaminar phospholipid + Lipoprotein – cytoplasmic membrane (fluid stage) without any sterol • Two membrane in Gram negative bacteria • Condensation at some points forming mesosome
21. Conti… 2) Outer to Cell Membrane – cell wall containing specialized unique chemicals called peptidoglycan 3) Outer to Cell Wall – investing layer either capsule/glycocalyx/slime layer 4) S layer – Single type protein lattice outer to CW
22. Characteristics of Prokaryotes • No genetic exchange during chromosome replication • Show secretory and excretory activities • Show chemical selectivity, motility and alteration of life stage (spore) • Wide range of temperature and pH tolerance • Heterogenous nutritional requirements and host specificity • Can produce self protective molecule bacteriocin • Become infected by particular virus • Can acquire extrachromosomal DNA (plasmid)
23. Difference Between Eukaryotes and Prokaryotes • Nature of Nucleus • Mitotic Division • Presence of histones in DNA • Membrane bound Organelles • Size of Ribosomes • Peptidoglycan in Cell Wall
24. Bacterial cells
25. Bacterial cells • essential structures – chemical composition – Organization – Functions • non-essential structures – chemical composition – Organization – Functions
26. Structures of bacteria • Essential Structures (maintain viability) – Cell Wall – Cell Membrane – Mesosome – Ribosome – Nucleoid – Periplasm
27. Structures of bacteria • Non-essential Structures (viability is not affected in their absence) – Flagella – fimbria (pili) – Capsule – Glycocalyx – slime layer – Plasmid – spore
29. Cell wall • Component – peptidoglycan (PG) – Teichoic acid – teichorunic acid – Polysaccharides – LPS – Lipoproteins • PG backbone: NAG and NAM • Tetrapeptide side chains attached to NAM • Interpeptide bridge
30. Conti… • Function – osmotic protection – integrity of cellular structures – virulence factors – Fully permeable to ions, aminoacids and sugars – makes it rigid – determines shape – Acts as antigen – Used as serological diagnosis
31. Peptidoglycan
32. Gram positive cell envelope • Covalently bound to the thick peptidoglycan are – teichoic acid (their backbones are usually phosphorus containing polymers of ribitol or glycerol) or – teichuronic acid (glucuronic acid- containing polysaccharides • negatively charged molecules concentrate metal ions from the surroundings
33. Conti… • Teichoic acids can also direct autolytic enzymes to sites of peptidoglycan digestion (autolysis). • This is needed to insert sections of cell wall for growth and division. • Lipoteichoic acid is primarily associated with the cell membrane.
34. The Gram negative cell envelope • Covalently linked to the thin peptidoglycan is the Braun lipoprotein which binds the outer membrane to the cell wall. • Like other membranes it contains proteins and phospholipids. • Unlike other membranes it contains lipopolysaccharide
35. Conti… • Lipopolysaccharide – helps to provide a permeability barrier • LPS consists of three regions – an outer O antigen – a middle core – an inner lipid A region • core contains several sugars – lipid A contains β hydroxyfatty acids (uncommon in nature) – The molecule displays endotoxin activity
36. Conti… • Porins in the outer membrane form channels to allow passage of small hydrophilic nutrients (such as sugars) through the outer membrane.
37. Cell membrane • Phospholipid bilayer – Except triple layer in Mycoplasma • Interspersed with lipoprotein • Selectively permeable
38. Cell Membrane • Functions – Transport – Synthesis – Excretion – Secretion – Metabolism – division by mesosome
39. Nucleoid • Double stranded coiled helical DNA molecule – remain in a single chromosome • no introns • no non-coding sequences • no regulatory sequence • no long terminal repeats (LTRs) • Operon present
40. Nucleoid • Function – bears genes and genetic characters – maintain metabolism
41. Ribosome • 70 s in sedimentation co-efficient • Aggregated • Function – Protein Synthesis
42. Non-essential structures • Flagellum/-a (long whip like) – Filamentous Protein Appendages – Composed of protein as flagellin unit – Arise from cytoplasmic membrane – Account for most bacterial motility – “Run and tumble” – Chemotaxis, phototaxis, aerotaxis, and magnetotaxis – Antigenic structure Fig 3.42
44. Non-essential structures Pilus/-i • Thin hair like appendages • Composed of protein as pillin subunit • Arise from cytoplasmic membrane • Function – Attachment – Conjugation – Acts as virulence factors – Antigenic
45. Capsule/Glycocalyx • External surface layer composed of polysaccharides Except – Polypeptide in Bacillus – Hyaluronic acid for Streptococci • Gel like • Forming either capsule (compact, complete and tight investing) or slime layer (loose meshwork) • Functions – prevent phagocytosis – Attachment of bacteria – Acts as Antigen
46. Plasmid • Extra-chromosomal Double stranded Circular DNA • Independent of replication • Types – Transmissible – non-transmissible • Function – Carries gene for its own replication – Carries gene antibiotic resistance factors – Carries gene Proteins & toxin
48. Endospores • Highly resistant structures formed at adverse environment • Composition – Bacterial DNA – small cytoplasm – cell membrane – Peptidoglycan – very little water – thick keratin like coat
49. Endospores • Highly resistant to – heat, moisture, chemicals, radiation and antibiotics • Special component – calcium salt of Dipicolinic acid • No metabolic activities, remain dormant for many years • Two events: sporulation and germination
50. The endospore
51. Steps of Sporulation
53. Classification of bacteria • Basis of Classification • differences between Gram positive and Gram negative bacteria • atypical characters of bacteria in relation to staining
54. Basis of Classification • Morphological Classification • Staining Properties • Thickness of Wall • According to Motility
55. Morphological Classification Morphology of Bacteria • Cocci – rounded or oval (Staphylococcus) • Bacilli – elongated rod like (Esch.coli) • Vibrio (from vibration) – coma shaped (Vibrio cholerae) • Spiral bacteria – long slender curved body with wave like spiral (Spirillum minus, Helicobacter pylori)
56. Others Shapes • Cocco-bacillus – longer than coccus, shorter than bacillus (Bordetella, Brucella) • Filamentous – long curved body like ribbon with branching (Actinomycetes, Nocardia)
62. Spirochaetes
63. Thickness of Wall • Rigid thick wall Bacteria – Free-Living (Extracellular) – Non-Free Living (Obligate Intracellular) • Flexible thin walled Bacteria – Treponema – Borrela – Leptospira • Wall-less Bacteria – Mycoplasma – Ureaplasma
64. Rigid thick wall Bacteria • Free-Living (Extracellular) – Gram Positive – Gram Negative – Acid-Fast • Non-Free Living (Obligate Intracellular) – Rickettsia – Chlamydia
65. Staining Properties • Gram Positive • Gram Negative • Acid-Fast Bacteria
66. Gram Positive Bacteria • Cocci – Streptococcus – Staphylococcus • Bacilli – Spore Forming • Bacillus – Non-spore forming • Clostridium • Corynebacterium • Listeria
67. Gram Negative Bacteria • Cocci – Neisseria gonorrhoae – Neisseria meningitidis • Bacilli – Enterobacteriaceae – Non-Enterobacteriaceae
68. According to Motility • Motile – Flagellated Bacteria – Non-Flagellated Bacteria • Non-Motile – All Cocci
69. Bacillus with peritrichous flagella
70. Morphological study of bacteria • Staining • Motility test
71. Staining Theoretical approach • Types • Laboratory procedures • findings of – Gram’s – Zeihl-neelsen (Z-N) – Albert’s staining
72. Types of Staining • Simple Staining • Differential Staining • Special Staining
73. Types of Staining Simple Staining • using a single dye – methylene blue – Leishman
74. Types of Staining Differential Staining • using primary and counter dye • performing a step of decolourisation • to see differential characters of bacteria – Gram’s stain – Ziehl-Neelsen stain – Albert stain
75. Types of Staining Special Staining • to see unique property of particular bacteria – Fluorescense stain
76. Gram’s staining • Named according to inventor Christian Gram • Based on the property of bacterial cell envelope • stained at first by a primary dye & mordanted • Decolorized by acetone or alcohol • Counter stain is added • Gram positive bacteria – can resist decolourisation and retain the primary dye • Gram negative bacteria – can not resist decolourisation and take the counter dye
77. Gram Positive Bacteria • Thick layer of Peptidoglycan • Negatively charged teichoic acid on surface • Polysaccharide
78. Gram Negative Bacteria • Cell wall much more complex • Thin peptidoglycan layer, filled and surrounded with periplasm (protein rich gel-like fluid) • Unique outer membrane on top – Bilayer, yet outer layer is LPS layer (lipid A and O specific polysaccharide) – LPS acts as endotoxin (lipid A) • Gram neg. bacteria are less sensitive to medications because outer membrane acts as additional barrier. Fig 3.34
79. Atypical cell envelope • Acid-fast and related bacteria – Mycobacteria – Nocardia • Presence of Mycolic acids – long, branch chained fatty acids
80. Gram un-stainable cell wall • Atypical peptidoglycan • Spirochaetes, Mycobacterium, – High lipid content – Tight fluid mosaic
83. Thank You